1. Field of the Invention
The present invention relates to oxygen barrier polyamide compositions exhibiting high oxygen scavenging capability suitable for extended shelf-life packaging applications. The polyamide products are particularly suited for producing barrier packaging articles such as monolayer or multi-layer films, sheets, thermoformed containers and coinjection/coextrusion blow molded bottles comprising polyethylene terephthalate (PET), polyolefin or polycarbonate as structural layers. Such articles are useful in a variety of oxygen-sensitive food, beverage, pharmaceutical, and health care product packaging applications.
2. Description of the Related Art
It is well known in the art to provide polyamide based packaging articles such as films, bottles and containers, which are useful for food packaging. Many such articles are made of multiple layers of different plastics in order to achieve the desired barrier properties. For example, U.S. Pat. Nos. 5,055,355 and 5,547,765 teach laminates of polyamides and ethylene vinyl alcohol, copolymers which have good oxygen barrier properties.
In order to enhance freshness preservation, it is standard practice to package food and other materials within laminated packaging material that generally includes a barrier layer, that is, a layer having a low permeability to oxygen.
The sheet material can be thin, in which event it is wrapped around the material being packaged, or it can be sufficiently thick that it forms a shaped container body. It is known to include an oxygen scavenger in sheet material. The oxygen scavenger reacts with oxygen that is trapped in the package or that permeates into the package. This is described, for instance, in U.S. Pat. Nos. 4,536,409 and 4,702,966. U.S. Pat. No. 4,536,409, for example, describes cylindrical containers formed from such sheet material.
Various types of oxygen scavengers have been proposed for this purpose. U.S. Pat. No. 4,536,409 recommends potassium sulfite as an oxygen scavenger. U.S. Pat. No. 5,211,875 discloses, the use of unsaturated hydrocarbons as oxygen scavengers in packaging films. It is known in the art that ascorbic acid derivatives as well as sulfites, bisulfites, phenolics, etc. can be oxidized by molecular oxygen, and can thus serve as an oxygen scavenging material. U.S. Pat. No. 5,075,362 discloses the use of ascorbate compounds in containers as oxygen scavengers. U.S. Pat. Nos. 5,202,052 and 5,364,555 describe polymeric material carriers containing oxygen scavenging material. These polymeric carriers for the oxygen scavenging material include polyolefin, PVC, polyurethanes, EVA and PET. U.S. Pat. Nos. 5,021,515, 5,049,624 and 5,639,815 disclose packaging materials and processes therefor which utilize a polymer composition which is capable of scavenging oxygen; such compositions include an oxidizable organic polymer component, preferably a polyamide (preferably MXD6) and a metal oxidation promoter (such as a cobalt compound). These compositions can be used with PET, for example.
U.S. Pat. No. 5,529,833 describes the use a composition comprising an ethylenically unsaturated hydrocarbon oxygen scavenger which is incorporated into a film layer and used for making packaging for oxygen sensitive products. The oxygen scavenger is catalyzed by a transition metal catalyst and a chloride, acetate, stearate, palmitate, 2-ethylhexanoate, neodecanoate or naphthenate counterion. Preferred metal salts are selected from cobalt (II) 2-ethylhexanoate and cobalt (II) neodecanoate. Because water deactivates the oxygen scavenger composition, the composition can only be used for packaging for dry materials.
There remains a need for the selection of a substrate which can provide oxygen scavenging in order to reduce the oxidation of the constituents contained therein. Accordingly, it is an object of the invention to provide an improved oxygen scavenging blend for use in coating substrates for food packaging applications.
The present invention provides a single polyamide layer which is an effective oxygen barrier as well as a multiple layered structure formed from the polyamide layer to provide even more effective oxygen barrier properties. These high oxygen barrier polyamide compositions exhibit unusually high oxygen scavenging capability suitable for extended shelf-life, packaging applications. The oxygen scavenging polyamide compositions may be prepared by a reactive extrusion process of compounding polyamides with a small amount of a low molecular weight, oxidizable polydiene or polyether polymer. The polyamide products are particularly suited to making barrier packaging articles which are useful in a variety of oxygen-sensitive applications.
The invention provides a polyamide composition which comprises a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether.
The invention also provides a polyamide composition which comprises a blend of a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether.
The invention further provides a polyamide composition which comprises the reaction product of a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether.
The invention still further provides a oxygen barrier film comprising a layer of a polyamide composition which comprises a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether.
The invention yet further provides a multilayer article which comprises an oxygen barrier polyamide composition layer comprising a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether; and a thermoplastic polymer layer on one or both sides of the polyamide composition layer.
The invention also provides a shaped article which comprises a polyamide composition which comprises a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether.
The invention further provides a process for producing a polyamide composition which comprises melting a polyamide homopolymer, copolymer, or blends thereof, and blending the molten polyamide homopolymer, copolymer, or blend thereof with at least one polyamide reactive, oxidizable polydiene or oxidizable polyether to form a mixture, and then cooling the mixture.
The invention also provides a process for producing an oxygen barrier polyamide film which comprises melting a polyamide homopolymer, copolymer, or blends thereof, and blending the molten polyamide homopolymer, copolymer, or blend thereof with at least one polyamide reactive, oxidizable polydiene or oxidizable polyether to form a mixture, and then extruding, casting or blowing the mixture into a film with subsequent cooling.
The invention also provides a process for producing an oxygen barrier polyamide film which comprises melting a composition comprising a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether, and then extruding, casting or blowing the composition into a film with subsequent cooling.
The invention also provides a process for producing a multilayer article which comprises melting a polyamide homopolymer, copolymer, or blends thereof, and blending the molten polyamide homopolymer, copolymer, or blend thereof at least one polyamide reactive, oxidizable polydiene or oxidizable polyether to form a mixture; separately melting a thermoplastic polymer composition; and then coextruding, casting, blowing, thermoforming, blow molding or coinjecting the mixture and thermoplastic polymer composition into a multilayer article, with subsequent cooling.
The invention also provides a process for producing a multilayer article which comprises melting a composition comprising a polyamide homopolymer, copolymer, or blends thereof, and at least one polyamide reactive, oxidizable polydiene or oxidizable polyether; separately melting a thermoplastic polymer composition; and then coextruding, casting, blowing, thermoforming, blow molding or coinjecting the mixture and thermoplastic polymer composition into a multilayer article, with subsequent cooling.